The inventive method is concerned very generally with the problem of authentication in computer systems which are connected with a plurality of data stations. The data stations can be computers with programs, personal computers or dedicated data stations. As soon as a user or subscriber wants to make connection with a computer through his data station he will be required by the computer to authenticate himself by a password. He transmits the password to the data station which passes it as information to the computer. The involved problem is that an unauthorized user can so modify his data station that he receives a copy of the information sent from the first data station to the computer and withdraws it from the data station. Thereafter the unauthorized user can be authenticated in place of the authorized user because he knows the password. A further problem of this type of authentication resides in that a privileged user who has unlimited access to the data in the computer can acquire the password of a user by reading it from the memory.
In a first known authentication method, in the password announcement the unencoded password is transmitted from the data station of the user to the computer system. There the password is encoded by means of a one-way function and stored in a data file. In usage of the password, that is in the authentication, the password sent in clear text from the data station to the computer system is likewise encoded in the computer system by a one-way function. By "one-way function" is meant a function which is easy to calculate but for which no method exists for calculating its reverse function at reasonable expense.
The resulting value is subsequently compared with the encoded password stored in the data file. Upon identity the user is taken as authenticated. In this method it is not possible to gain knowledge of the password by reading out the password data file. However, the password transmitted in clear text to the computer system can be tapped and subsequently improperly used.
An improvement can be achieved if the authentication takes place in a dialog between the data station and the computer system. In connection with this it has already been proposed to provide a symmetrical ciphering process. In it in the announcement of the password 20 the password is stored in a protected data file in clear text. For authentication a random number is created in the computer system by a random number generator, which random number is encoded by an encoding unit and sent to the data station. This information is decoded in a decoder with the password submitted by the user, is modified by an addition, encoded with the password by the encoder, and returned to the computer system. In the computer system the information is decoded by a decoder and compared with the random number likewise modified by the addition, which must result in equality using a comparator. A disadvantage of this solution is likewise that the password is obtainable by a privileged user, such as a system manager or equipment technician, who can read out the corresponding data file. Therefore in this case the password can also be stolen
Finally, a method has also been developed that requires the storage of at least two values from the user. These keys are created by a keying central unit according to a given method and are not freely selectable by the user, so that the user cannot choose a mnemonic password as in customary password systems. Since the user for security reasons is not permitted to write down the password, this method is practical only in connection with chip cards.
The invention has as its object the provision of a method of the previously mentioned type which offers higher security with simple handling.